Use of electron beam irradiation for mold decontamination on cheddar cheese.

Cheddar cheese slices, surface-inoculated with either Penicillium cyclopium or Aspergillus ochraceus spores, were vacuum packaged and irradiated using an electron beam accelerator. Following treatment at .21 and .52 kGy, the shelf-life of cheese containing P. cyclopium was extended by 3 and 5.5 d, respectively, in comparison with inoculated, untreated samples. Under similar treatment and storage conditions, cheese containing A. ochraceus exhibited average shelf-life extensions of 42.5 and 52.2 d, respectively. Increasing the postirradiation storage temperature to 15 degrees C reduced the shelf-life of cheese, especially with samples containing A. ochraceus. The lowest dose required to inactivate ca. 50 to 60 spores/cm2 of either A. ochraceus or P. cyclopium on the surface of cheese was ca. .42 and .95 kGy, respectively. Irradiation survival curves of A. ochraceus and P. cyclopium spores in cheese yielded average values (the dose required to reduce initial population by 90%) of .21 and .42 kGy, respectively.

Microbiological and Other Characteristics of Chicken Breast Meat Following Electron-Beam and Sous-Vide Treatments.

The combined effects of radiation and sous-vide treatment of chicken breast meat were investigated with respect to survival and growth of Listeria monocytogenes , shelf life, thiamine content, and sensory qualities. Chicken breasts were inoculated with L. monocytogenes 81-861 (105 CFU/g), vacuum-packed, irradiated with electron beam (EB) up to 2.9 kGy, and cooked to an internal temperature of 65.6°C. Sous-vide treatment alone had marginal lethal effect on the L. monocytogenes ; the residual inoculum reached 107 CFU/g after 8 weeks at 2°C. However, after the combined treatments of sous-vide and EB at 2.9 kGy, the organism remained undetectable during the 8-week storage period. Parallel studies on uninoculated breast meat revealed that sous-vide samples had a shelf life of less than 6 weeks without EB treatment, whereas samples that were irradiated and then received sous-vide treatment had a shelf life of at least 8 weeks. There was a slight reduction in thiamine levels as a result of the EB treatment, but there was essentially no additional loss of thiamine due to the subsequent sous-vide treatment and storage at 2°C. Electron-beam treatment had very little effect on the odor and flavor of the reheated samples. It was concluded that EB treatment combined with sous-vide treatment can greatly enhance the microbial safety and shelf life of chicken breast meat.

Peptidases from two strains of Pseudomonas fluorescens: partial purification, properties and action on milk.

Pseudomonas fluorescens strains 240 and 32A expressed cell-associated peptidase activity which was shown by subcellular fractionation to be primarily intracellular. Two peptidases were partly purified from strain 32A. One specifically hydrolysed N-alpha-benzoyl-DL-arginine-4-nitroanilide and was termed endopeptidase and the other hydrolysed L-lysine- and L-leucine-4-nitroanilide and was termed aminopeptidase. The endopeptidase had very low activity on bovine serum albumin compared with that of trypsin and probably was not a proteinase. The endopeptidase had a mol. wt of 33,000 and a pH optimum of 8.0. The enzyme was stimulated by Ca2+ and Mg2+ and inhibited by Co2+, Mn2+, Hg2+, Zn2+ and leupeptin. Soya bean trypsin inhibitor and phenylmethane sulphonyl fluoride (PMSF) had no effect on its activity. The aminopeptidase had a mol. wt of 44,000 and a pH optimum of 8.0. It was inhibited by all the metal ions mentioned above and by PMSF. Little proteolysis was found when ultra high temperature (UHT) sterilized milk was treated with cell-free extract from strain 32A. It was concluded that the cell-associated peptidases from Pseudomonas strains normally present in raw milk may not contribute significantly to the deterioration of UHT sterilized milk.

Influence of iron(III) and pyoverdine on extracellular proteinase and lipase production by Pseudomonas fluorescens B52.

Factors associated with the production of extracellular lipase and proteinase by Pseudomonas fluorescens B52 during the late-log, early-stationary phase of grown were examined. Active lipase production by resting cell suspensions was observed when cells were harvested during the log phase (A600 of 0.3-0.9). Resting suspensions of younger cells (A6000 less than 0.1) synthesized lipase after a significant lag. Addition of cells of the proteinase- and lipase-deficient mutant P. fluorescens RM14 to B52 cells at low density resulted in stimulation of lipase and proteinase production. Similar results were found using cell-free culture fluid of RM14. Gel filtration on Biogel P2 revealed that the stimulatory factor co-chromatographed with the iron(III) siderophore, pyoverdine. Partially purified pyoverdine stimulated enzyme synthesis at a concentration of 6 microM while having no effect on activity of preformed enzyme. Production of pyoverdine and extracellular enzymes was also stimulated by transferrin, a strong iron(III) binding protein. Growth of B52 in deferrated media was limited to 27% of that found with untreated media. Maximum pyoverdine, proteinase and lipase synthesis was obtained at a final iron(III) concentration of 5.75 microM. Growth was maximal in 8.75 microM iron(III) while synthesis of pyoverdine, proteinase and lipase was reduced to 3.6, 6.6 and 30% respectively in 23.75 microM iron(III). Lipase activity in cell-free culture fluid was slightly inhibited by the addition of up to 400 microM iron(III) while proteinase activity was unaffected. In dilute cell suspensions, lipase synthesis was more sensitive to iron(III) than was proteinase (50% inhibition at 1.6 microM and a maximum of 40% inhibition at 5.0 microM, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of a chymosinlike protease from the gastric mucosa of harp seal (Pagophilus groenlandicus).

Four zymogens of acidic proteases A, B, C, and D were isolated from the gastric mucosa of harp seals by ion-exchange chromatography on a diethylaminoethyl-Sephadex A-50 column. The major zymogens were A and C, and the ratio of zymogen A to zymogen C was greater in extracts from 1-week-old animals than in extracts from adult animals. Zymogens A and C were further purified by affinity chromatography using carbobenzoxy-D-phenylalaninetriethylene tetramine Sepharose and gel filtration on a Sephadex G-100 column. Certain physical and catalytic properties of proteases A and C were compared with those of calf chymosin (EC 3.4.23.4) and porcine pepsin (EC 3.4.23.1). Zymogen C and the corresponding enzyme were homogeneous on analytical polyacrylamide gel electrophoresis. Zymogen A was homogeneous as judged by sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis and high performance liquid chromatography, but was heterogeneous by polyacrylamide gel electrophoresis at pH 8.3. Zymogens A and C had molecular weights of 33 800 and 44 000, respectively, as estimated by SDS-polyacrylamide gel electrophoresis. Protease A had an isoelectric point of 4.90. Protease A was similar to calf chymosin with respect to several criteria. It had a higher ratio of milk-clotting to proteolytic activity than those of seal protease C and porcine pepsin and had a pH optimum of 2.2-3.5 for hemoglobin hydrolysis. It did not inactivate ribonuclease, had very low activity on N-acetyl-L-phenylalanyl-3,5-diiodo-L-tyrosine and lost activity in 6 M urea. These results indicate protease A is chymosinlike.